The bar example is a still a bit vexing to me, because it's the sort of problem/solution I often see brought up as an example, but I still fail to see the utility. A digital signature (e.g. PGP) already can act as a certificate of authenticity from a trusted party and all you need is their public key. Could you explain what the blockchain improves about that, or what it solves in that application that digital signatures don't already?